Interest in the use of terahertz (THz) detectors outside of a laboratory for space, atmospheric, and terrestrial applications has grown immensely in the past half century. Of particular interest in recent years is the development of a quantum cascade laser (QCL) as a THz frequency source. Attractive features of the THz QCL include high output power (greater than 100 mW), a good wall-plug efficiency, spectral purity, stability, compactness, and reliability. A QCL operating in the range of 1.2 to 4.9 THz has been demonstrated. A multimode QCL can be designed to operate at frequency below 1.2 THz. However, accurate and reliable tuning of the QCL emission to select one or more single-mode frequencies is essential for most applications and is still an issue.
A number of approaches for tuning the emission from a THz QCL, which may use temperature, electrical (current/voltage), resonant cavity or mechanical methods for frequency and mode selection, are currently being investigated. All of these approaches have one or more negative features. For example, these approaches limit range of tuning, have high cost, are very complex, and lack thermal and vibrational stability. These limitations adversely affect commercialization and use in a large variety of potential applications such as remote sensing, spectroscopy, heterodyne receiver, security screening, and bio-medicine.
Thus, an alternative approach may be beneficial.